W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C OU N C I L

Effect of Thermal Generation Replacement on System Frequency

ResponseEnoch Davies, PE

Staff Engineer

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W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C OU N C I L

Purpose of Study

• Changing carbon emission reduction policies– State Renewable Portfolio Standards– EPA has a number of existing and proposed

emission policies• EPA 111(d) is a proposal to reduce carbon emissions for

existing generators on a state-by-state basis

• Concern over affect of carbon emission reductions on system frequency response

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W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C OU N C I L

Study Assumptions

• Study ONLY considered system frequency response• 2023 Heavy Summer Base Case was used as the base

line for system frequency response– California once through cooling assumptions were largely

included• Generation replacements were based on

– Assumptions from Transmission Expansion Planning Policy Committee (TEPPC) Common Case

– Assumptions from the EPA 111(d) proposal• Units replaced were least efficient as identified through the

Common Case

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Study Assumptions (cont)

• Replacement generation was based on– The resource type with the most limited amount of

frequency response (inverter-based technologies)• Pseudo inertial or governor response was not considered

• No changes were made to base case area interchanges

• Double Palo Verde generator outage used for frequency response comparison

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Generator Type Frequency Response Comparison

0 5 10 15 20345

350

355

360

365

370

375

380

385

390

Base Load ThermalInverter Based Renewable Responsive Thermal

Time(sec)

Pow

er G

ener

ated

(MW

)

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Case Development

• Two scenarios were selected– 1: Used TEPPC common case assumptions for

initial thermal generation replacement followed by EPA 111(d) assumptions to achieve levels for the proposed rule

– 2: Focused on the southwest and reductions were based on task force provided assumptions of the EPA 111(d) proposed rule

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W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C OU N C I L

Case Development (cont)

• Case Changes– San Onofre Nuclear Generation Station (SONGS)• Turned off in case and generation replaced by existing

generation present in the case (~2100MW)

– Two scenarios examined – removed large amounts of thermal generation• Scenario 1: 7146 MW replaced• Scenario 2: 6369 MW replaced

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W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C OU N C I L

Case Development (cont)

• Scenario 1• Used inverter based generator model (WT4G)• Replaced the stability model for each of the thermal

generating units selected with out making any changes to the power flow data

• Scenario 2• The task force recommendations were

– Thermal units to replace– Location of replacement

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W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C OU N C I L

Scenario 1 Results

0 5 10 15 2059.75

59.8

59.85

59.9

59.95

60

60.05

2023 Base CaseScenario 1 Simulation

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Scenario 2 Results

0 5 10 15 2059.75

59.8

59.85

59.9

59.95

60

60.05

2023 Base CaseScenario 2 Simulation

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Conclusions

• The two scenarios examined did not show a significant change in system frequency response from the original base case

• Thermal units replaced were primarily unresponsive to frequency deviations (blocked governor response)

• The generation replaced was a small portion of the total generation online in the case (~3.5%)